Upregulation of HIF-1α protein induces mitochondrial autophagy in primary cortical cell cultures through the inhibition of the mTOR pathway

Abstract

Cerebral ischemia/reperfusion (I/R) can induce neuronal death, particularly in the hippocampal formation (HF). Molecular genetic studies have suggested that the activities of the transcription factor, hypoxia-inducible factor-1α (HIF-1α), are closely linked to ischemia-induced neuronal death. However, the mechanisms through which HIF-1α functions remain poorly understood. In this study, primary cortical neurons were subjected to oxygen-glucose deprivation (OGD) to establish a cell model of OGD/reperfusion (RP). HIF-1α mRNA and protein expression was measured by qRT-PCR and western blot analysis. Cell proliferation was detected by MTT assay. Flow cytometric analysis was used to detect cell apoptosis and changes in mitochondrial mass. The expression of LC3-I and LC3-II was examined by western blot analysis. We found that HIF-1α increased cell proliferation and decreased cell apoptosis in our cell model of OGD/RP using cultured neonatal rat cortical neurons. The overexpression of HIF-1α significantly induced changes in mitochondrial mass and mitochondrial autophagy in cortical neurons. Moreover, the inhibition of HIF-1α markedly suppressed cell proliferation and mitochondrial autophagy. We also demonstrated that the HIF-1α-induced mitochondrial autophagy was accompanied by the inhibition of the mTOR pathway. This study provides direct in vitro evidence that HIF-1α overexpression triggers mitochondrial autophagy, thereby increasing neuronal survival. Our results highlight a novel target molecule toward which anti-ischemic neuroprotective effects can be applied.